work around issues writing to Windows clipboard

https://anki.tenderapp.com/discussions/beta-testing/1014-cannot-copy-from-fields-in-anki-210beta36

aqt/editor.py

@@ -21,7 +21,7 @@ from anki.hooks import runHook, runFilter
 from aqt.sound import getAudio
 from aqt.webview import AnkiWebView
 from aqt.utils import shortcut, showInfo, showWarning, getFile, \
-    openHelp, tooltip, downArrow
+    openHelp, tooltip, downArrow, showCritical
 import aqt
 from bs4 import BeautifulSoup
 import requests
@@ -903,6 +903,36 @@ class EditorWebView(AnkiWebView):
             return
         html = mime.html()
         mime.setHtml("<!--anki-->" + html)
+        if isWin:
+            self._windowsSetMimeData(clip, mime)
+        else:
+            clip.setMimeData(mime)
+
+    def _windowsSetMimeData(self, clip, mime):
+        import win32clipboard, time
+        from ctypes import windll
+
+        grabbed = False
+        for i in range(10):
+            try:
+                win32clipboard.OpenClipboard(self.editor.parentWindow.winId())
+                grabbed = True
+                break
+            except:
+                time.sleep(0.01)
+                continue
+
+        if not grabbed:
+            hwnd = win32clipboard.GetOpenClipboardWindow()
+
+            longpid = ctypes.c_ulong()
+            result = windll.user32.GetWindowThreadProcessId(hwnd, ctypes.byref(longpid))
+            pid = longpid.value
+
+            showCritical(_("Unable to access clipboard - locked by process %d" % pid))
+            return
+
+        win32clipboard.CloseClipboard()
         clip.setMimeData(mime)
 
     def contextMenuEvent(self, evt):